1. Field of the Invention
The present invention relates generally to an area light source device and a liquid crystal display device that includes the area light source device, and more particularly to an area light source device in which an L-shaped light source and a wedge-shaped light guide are combined.
2. Description of the Related Art
Liquid crystal display devices have been applied to various fields as display devices for, e.g. OA equipment such as computers and TVs, taking advantage of their features of light weight, small thickness and low power consumption. In recent years, the liquid crystal display devices have also been used as display devices of mobile terminals such as mobile phones. This type of liquid crystal display device includes, for example, a liquid crystal display panel and an area light source device that illuminates the liquid crystal display panel.
As regards the liquid crystal display device with this structure, it has been proposed to adopt an L-shaped light source for enhancing the luminance of the area light source device, and a wedge-shaped light guide for reduction in thickness and weight (see Jpn. Pat. Appln. KOKAI Publication No. 9-178948, for instance).
In such structure as described in the above document, however, it is difficult to efficiently guide emission light from the light source to the light guide. Specifically, since the wedge-shaped light guide is adopted, the incidence surface of the light guide, which is opposed to the light source, has a trapezoidal shape corresponding to the wedge-shaped cross section and has a width (height) gradually decreasing toward a thin part of the light guide. Consequently, in the thin part, the ratio in amount of incident light from the incidence surface to emission light from the light source is considerably low, and a sufficiently high luminance may not be obtained.